Assessing the Energy Resilience of Office Buildings

buildings Article Assessing the Energy Resilience of Office Buildings: Development and Testing of a Simplified Metric for Real Estate Stakeholders Paul Mathew * , Lino Sanchez, Sang Hoon Lee and Travis Walter Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; [email protected] (L.S.); [email protected] (S.H.L.); [email protected] (T.W.) * Correspondence: [email protected] Abstract: Increasing concern over higher frequency extreme weather events is driving a push towards a more resilient built environment. In recent years there has been growing interest in understanding how to evaluate, measure, and improve building energy resilience, i.e., the ability of a building to provide energy-related services in the event of a local or regional power outage. In addition to human health and safety, many stakeholders are keenly interested in the ability of a building to allow continuity of operations and minimize business disruption. Office buildings are subject to significant economic losses when building operations are disrupted due to a power outage. We propose “occupant hours lost” (OHL) as a means to measure the business productivity lost as the result of a power outage in office buildings. OHL is determined based on indoor conditions in each space for each hour during a power outage, and then aggregated spatially and temporally to determine the whole building OHL. We used quasi-Monte Carlo parametric energy simulations to demonstrate how the OHL metric varies due to different building characteristics across different climate zones and Citation: Mathew, P.; Sanchez, L.; seasons. The simulation dataset was then used to develop simple regression models for assessing the Lee, S.H.; Walter, T. Assessing the Energy Resilience of Office Buildings: impact of ten key building characteristics on OHL. The most impactful were window-to-wall ratio Development and Testing of a and window characteristics. The regression models show promise as a simple means to assess and Simplified Metric for Real Estate screen for resilience using basic building characteristics, especially for non-critical facilities where it Stakeholders. Buildings 2021, 11, 96. may not be viable to conduct detailed engineering analysis. https://doi.org/10.3390/ buildings11030096 Keywords: energy resilience; resilience metrics; building habitability; passive survivability; office buildings Academic Editor: Ravi Srinivasan Received: 17 December 2020 Accepted: 24 February 2021 1. Introduction Published: 5 March 2021 Resilience in the context of the built environment is commonly described as the ability to prepare for and adapt to changing conditions and withstand and recover rapidly Publisher’s Note: MDPI stays neutral from disruptions [1]. Increasing concern over higher frequency extreme weather events with regard to jurisdictional claims in is driving a push towards a more resilient built environment. In recent years there has published maps and institutional affil- iations. been growing interest in understanding how to evaluate, measure, and improve building energy resilience, i.e., the ability of a building to provide energy-related services in the event of a local or regional power outage caused by or coupled with events such as extreme heat and cold, wildfires, earthquakes, hurricanes, and floods [2,3]. Energy-related services include the provision of lighting, heating, ventilation and air conditioning (HVAC), and Copyright: © 2021 by the authors. plug power. The building design community is looking to address these issues in new and Licensee MDPI, Basel, Switzerland. retrofit construction; owners and operators need to assess and improve the energy resilience This article is an open access article of their buildings, and private-sector intermediaries such as the insurance industry are distributed under the terms and conditions of the Creative Commons financially vulnerable to these impacts and are potential partners in loss mitigation [4]. Attribution (CC BY) license (https:// Even in developed countries with a mature and reliable electrical grid, many buildings creativecommons.org/licenses/by/ are subject to power outages due to extreme events. For example, millions of people 4.0/). in California were affected by power outages lasting several days due to wildfires that Buildings 2021, 11, 96. https://doi.org/10.3390/buildings11030096 https://www.mdpi.com/journal/buildings Buildings 2021, 11, 96 2 of 20 triggered a precautionary shutdown of some transmission lines. Similarly, extreme winter weather and ice storms in many parts of the United States periodically cause days-long power outages for homes and businesses. Energy resilience is a critical component of overall building resilience, and is distinct from structural resilience, or resilience against human-created threats. Human safety and health are naturally the first priority driver for resilience. Beyond that, many stakeholders are keenly interested in the ability of a building to provide a safe and comfortable indoor environment to allow continuity of operations and minimize business disruption. Buildings such as offices, retail, food service, and sales, while not mis- sion critical like hospitals and public safety buildings, are subject to significant economic losses should building operations be halted due to a power outage. Financial losses due to disrupted business functions may outweigh any costs associated with structural damage. This was the case for numerous buildings after Hurricane Sandy, where insurance pay- ments for lost business were generally more significant than reconstruction expenses [5,6]. These considerations are increasing the interest in energy resilience from building owners, operators, and insurers. One of the primary challenges with energy resilience is that this concept is still loosely defined and not well characterized. Resilience is sometimes presented in tandem with large- scale sustainability efforts [7]. Numerous standards and guidelines for occupant comfort and energy efficiency already exist [8], including through the LEED (Leadership in Energy and Environmental Design) rating system’s passive survivability credit [9]. However, there are no widely-accepted aggregate metrics for energy resilience. This paper proposes a simple aggregate metric that serves as a first-order measure of building energy resilience, especially as it relates to business continuity in commercial buildings such as offices. We first provide a background of the relevant literature. Next, we define and describe the proposed metric. We show the application of the metric in a parametric energy simulation analysis. We then describe the viability of computing the metric based on easily obtainable building features. We conclude with limitations and areas for further research. 2. Background Much of the literature on building-level metrics for resilience is focused on the continuity of building operations for whole communities during a disruption or disaster [10–12]. The literature on energy resilience indicates that there are currently no universally agreed- upon metrics for assessing the energy resilience of individual buildings [13]. Various conceptual frameworks have been developed as methods for strategically organizing relevant resilience priorities and data requirements to inform the most appropriate metrics for determining resilience, including matrices [14], workflow charts [15], and decision trees [16]. However, while these frameworks offer stakeholders an approach to thinking through the process of resilience measurement, they do not include explicit energy resilience metrics for individual buildings. A resilience index developed by [17] quantifies the resilience of a building as a function of “robustness, resourcefulness, and recovery” within the context of maintaining building functionality when faced with unique hazards. An “energy provision” metric developed by [18] assesses the ability of a building to provide energy during a disruption, with more specific metrics including natural/mechanical ventilation potential, air filtration, and daylight coverage. Criteria-based building resilience and sustainability rating systems and certifications, such as LEED [19], RELi 2.0 [20], US Resiliency Council Building Rating System [21], and BREEAM (Building Research Estab- lishment Environmental Assessment Method) [22] aim to assess building resilience mostly through “feature-based” verification [23], which provides a prescriptive path to resilience, but does not necessarily take the form of explicit resilience metrics. A key concept emerging in building energy resilience is “passive survivability”, which denotes the ability of buildings to keep occupants safe and comfortable during a power outage [24]. “Thermal autonomy” has been proposed to assess a building’s potential to keep occupants at acceptable temperatures, with the metric ultimately consisting of Buildings 2021, 11, 96 3 of 20 the time occupants are kept in these sufficient thermal conditions [24,25]. Similarly, as another time-based metric, “hours of safety” has been proposed as a metric to assess the potential of a building to keep people safe from extreme cold and heat during a power outage, attributing resilience to the performance of thermal comfort-associated building components, such as insulation [26]. Other approaches for measuring building energy resilience is to group buildings with infrastructure systems by their role in infrastructural resilience [11]. Buildings are viewed as components of the larger power grid system, contributing to grid resilience,

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